1. Field of the Invention
The present invention relates to a regenerator formed by stacking a film-shaped resin material, an apparatus for manufacturing the regenerator, and a Stirling refrigerator provided with the regenerator.
2. Description of the Related Art
In recent years, Stirling engines have attracted attention from the standpoint of energy saving, environmental protection and the like. The Stirling engine is an external combustion engine that realizes a reversible, Stirling cycle utilizing an external heat source, which is advantageous in terms of energy saving and low pollution compared to the internal combustion engine that requires fuel excellent in inflammability as well as ignitionability such as gasoline.
A Stirling refrigerator is widely known as an application of the Stirling engine. The Stirling refrigerator uses a reversed Stirling cycle to generate cryogenic temperatures. Hereinafter, a structure of the Stirling refrigerator is explained with reference to the drawings.
As shown in FIG. 22, a Stirling refrigerator includes a cylinder 20 having an interior filled with an inactive gas such as hydrogen or helium as the working gas. Fitted in cylinder 20 are a piston 27 and a displacer 26, which divide the space within cylinder 20 into a compression space 28 and an expansion space 29. Piston 27 is driven by a linear motor 30. Piston 27, connected via a spring 32 to a body casing 23, periodically moves in cylinder 20 in a sinusoidal manner. Displacer 26, receiving the force of the sinusoidal movement of piston 27, reciprocates in cylinder 20. Since displacer 26 is also connected via a spring 31 to body casing 23, it periodically moves in a sinusoidal manner. In a normal operation, the sinusoidal movements of piston 27 and displacer 26 occur at the same period, with a constant phase difference.
A regenerator 15 is arranged between compression space 28 and expansion space 29. The two spaces are connected to each other via regenerator 15, to constitute a closed thermal circuit within the refrigerator. A heat-dissipation heat exchanger 24 is attached to the compression space 28 side of the closed thermal circuit, and a heat dissipater 22 is provided next to heat-dissipation heat exchanger 24. A heat-absorption heat exchanger 25 is attached to the expansion space 29 side of the closed thermal circuit, and a heat absorber 21 is provided next to heat-absorption heat exchanger 25.
The working gas within the closed thermal circuit flows in accordance with the movements of piston 27 and displacer 26, to realize the reversed Stirling cycle. Here, heat dissipater 22 serves to radiate heat within compression space 28 to the outside, and heat-dissipation heat exchanger 24 accelerates the radiation. Heat absorber 21 serves to absorb the external heat into expansion space 29, and heat-absorption heat exchanger 25 promotes the heat absorption.
An operation of a Stirling refrigerator having the above-described configuration is now explained. Firstly, linear motor 30 is activated to drive piston 27. Piston 27 driven by linear motor 30 approaches displacer 26, thereby compressing the working gas within compression space 28. Although this increases the temperature of the working gas within compression space 28, the heat generated in compression space 28 is rejected to the outside by heat dissipater 22 via heat-dissipation heat exchanger 24, so that the working gas within compression space 28 is maintained at approximately a constant temperature. This constitutes the isothermal compression process of the reversed Stirling cycle.
Next, the working gas compressed by piston 27 within compression space 28 flows, by its own pressure, into regenerator 15 and further to expansion space 29. At this time, the heat of the working gas is accumulated in regenerator 15. This constitutes the isochoric cooling process of the reversed Stirling cycle.
Subsequently, the high-pressure working gas flown into expansion space 29 expands, with displacer 26 moving downward. Although the temperature of the working gas within expansion space 29 lowers, the external heat is introduced into expansion space 29 by heat absorber 21 via heat-absorption heat exchanger 25, so that the interior of expansion space 29 is maintained at approximately a constant temperature. This constitutes the isothermal expansion process in the reversed Stirling cycle.
As displacer 26 begins to move upward, the working gas within expansion space 29 passes through regenerator 15 and returns to compression space 28. At this time, the heat having been accumulated in regenerator 15 is transferred to the working gas, thereby increasing the temperature of the working gas. This constitutes the isochoric heating process of the reversed Stirling cycle.
The sequence of processes (of isothermal compression—isochoric cooling—isothermal expansion—isochoric heating) is repeated to constitute the reversed Stirling cycles. As a result, heat absorber 21 gradually cools down, to finally reach a cryogenic temperature.
The regenerator is now explained in detail. The regenerator is a kind of heat exchanger, as described above, which transmits the heat to and from the working gas flowing therein. As such, it is necessary to secure a greater contact area with the working gas within the limited space. A complicated passage configured to secure the large contact area, however, will increase resistance with respect to the flow of the working gas, leading to degradation in efficiency of the Stirling refrigerator. That is, it is preferable for the internal structure of the regenerator that the heat transfer area in contact with the working gas is large while the flow resistance is low. Accordingly, a variety of fin structures have conventionally been proposed for the regenerator.
Among them, a regenerator formed by winding a film-shaped resin member (hereinafter, also simply referred to as “resin film”) into a cylindrical shape is known (see, e.g., Japanese Patent Laying-Open No. 2000-220897). FIG. 23A is a developed view of such a generator formed by winding a resin film in to a cylindrical shape. FIG. 23B is an end face view of the resin film in an unfolded state. FIG. 24A is a developed view of another regenerator formed by winding a resin film into a cylindrical shape, and FIG. 24B is an end face view of the other generator in an extended state. As shown in the figures, the regenerator of this type is provided with a plurality of dimples 41, 42 on one side of the sheet of resin film 8. When resin film 8 having dimples 41, 42 formed thereon are wound, gaps are formed between the layers of the resin film. The stacked layers of the resin film are separated from each other, thereby constituting part of the flow passage for the working gas.
Conventionally, dimples 41 of the regenerator of this type have been formed either by bonding spacers as additional members at regular intervals on a surface of resin film 8 extended in a sheet, or by performing silkscreen printing at regular intervals on a surface of resin film 8 extended in a sheet.
Production of a regenerator of this configuration is much easier than in the case of providing metallic fins. The cost required for production of the generator is considerably reduced as well. It is noted that the surface of the sheet resin film is often coated with a metal material, to improve heat exchange efficiency of the regenerator.
In general, the dimples formed on the surface of the resin film take a regular pattern from the standpoint of ease of manufacture. For example, dimples 41 are often arranged in stripes on resin film 8 as shown in FIG. 23A, or in a matrix as shown in FIG. 24A.
A way of mounting the regenerator configured as above to a Stirling refrigerator having the above-described structure is now explained. Referring to FIG. 25, a regenerator 15 to be incorporated into the Stirling refrigerator is formed with a resin film 8 wound around a bobbin (also called a stuffer) 14 constituting part of a cylinder 20 in which a displacer is fitted. Resin film 8 may have a part secured to bobbin 14, or may be wound freely without being secured.
Regenerator 15, configured by winding resin film 8 around bobbin 14, is inserted in an outer case 33 mounted in advance to a case body 23. In this case, regenerator 15 may be arranged such that the axis line of wound resin film 8 is approximately parallel to the flow direction of the working gas, to enable the working gas to flow within the flow passage formed by the projections as described above. Further, a heat absorber 21 is attached from above, so that a closed circuit is formed in the Stirling refrigerator, with regenerator 15 secured in place.
In the case where the projections are formed by bonding spacers to the surface of the resin film, the work is very burdensome. Generally, very fine spacers are bonded to the surface of the resin film in order to secure a greater heat transfer area with the working gas within the regenerator. This involves various problems that the bonding work in itself is troublesome, that accuracy of bonding position is low, that dust or dirt may be introduced during the bonding work, and that the use of an adhesive cannot guarantee high reliability over a long period of time.
In the case where the projections are formed by silkscreen printing on the surface of the resin film, the manufacturing cost increases due to the necessity of additional equipment for printing, drying and others. It is also very difficult to control the position, size, shape and the like of the projections with the silkscreen printing.
Further, conventional regenerators formed by winding resin film have projections always regularly arranged on the surface of the resin film. This disadvantageously simplifies the flow of the working gas through the regenerator, making it difficult to obtain high heat exchange efficiency.